Arrangement for de-icing a transparent window with an electric heating device

ABSTRACT

Arrangements for de-icing a transparent window, in particular a vehicle windshield, with an electric heating device, are described. The de-icing a transparent window has the following steps: Step A): Measuring a window temperature before an initial application of a heating voltage; Step B): Measuring the window temperature after a beginning of a heating period; and Step C): Applying a heating voltage of more than 100 volts to a heating device over a heating period of a maximum of 2 minutes, in particular a maximum of 90 seconds, and repeating step B).

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of the U.S.application Ser. No. 13/983,024 filed on Oct. 17, 2013 which is the USnational stage of International Patent Application PCT/EP2012/053561filed on Mar. 1, 2012 which, in turn, claims priority to European PatentApplication EP 11159257.2 filed on Mar. 22, 2011, all of which areincorporated herein by reference in their entirety.

DESCRIPTION

The invention is in the area of motor vehicle technology and relates toa method and an arrangement for de-icing a transparent window with anelectric heating device.

Transparent windows with an electric heating layer are well known per seand have already been described many times in the patent literature.Reference is made merely by way of example in this regard to the Germanpublished patent applications DE 10 2007 05286, DE 10 2008 018147 A1,and DE 10 2008 029986 A1. In motor vehicles, they are often used aswindshields since, by law, the central visual field must have nosubstantial vision restrictions. By means of the heat generated by theheating layer, condensed moisture, ice, and snow can be removed within ashort time.

The heating current is usually introduced into the heating layer via atleast one pair of strip-shaped electrodes (“bus bars”), which, ascollecting conductors, distribute the heating current over a wide front.The sheet resistance of the heating layer is relatively high with thematerials currently used in industrial series production and is on theorder of a few ohms. In order to nevertheless obtain adequate heatingpower for practical application, the heating voltage must be adequatelyhigh, whereas in internal combustion engine driven motor vehicles, thecurrently standard available onboard voltage is from 12 to 24 volts.

The Canadian patent application CA 2,079,175 presents a method for theelectrical heating of a window, wherein a feed voltage is applied whenthe window temperature drops below a certain value. The duration of theheating periods is adjustable as a function of the window temperaturebefore the beginning of the window heating. The window is then heateduntil a predefined window temperature is exceeded. The windowtemperature to be reached by heating is not restricted.

The European Patent application EP 0256 690 presents a method for theelectrical heating of a window with different feed voltages, with ahigher feed voltage used for de-icing and a lower feed voltage used fordefogging. The window heater is turned off at a critical windowtemperature.

The German Patent application DE 10313464 A1 teaches a method for windowheating, wherein the electrical energy supplied to a rear window heateris adjusted as a function of the window temperature. Upon reaching athreshold value for the rear window temperature, the window heater isturned off.

In contrast, the object of the present invention consists inadvantageously improving conventional methods for de-icing transparentwindows using an electric heating device. This and other objects areaccomplished according to the proposal of the invention by means of amethod and an arrangement with the characteristics of the coordinatedclaims. Advantageous embodiments of the invention are indicated by thecharacteristics of the subclaims.

According to the invention, an arrangement and a method for de-icing atransparent window, in particular a motor vehicle windshield, with anelectric heating device are presented.

The (window) arrangement according to the invention comprises atransparent window with an electric heating device, which can bedesigned in a variety of ways, for example, in the form of thin heatingwires, which serve as linear heating elements. Preferably, but notmandatorily, the electric heating device is a transparent electricheating layer (panel heater), which extends over a substantial part ofthe window area, in particular over its central visual field. Theheating device can be or is electrically connected via electricalconnection means to a voltage supply device for providing a feed voltageor a heating voltage. In the case of an electric heating layer, theconnection means comprise at least two connection electrodes, whichserve to introduce the heating current into the heating layer and areelectrically connected to the heating layer such that after applicationof the feed voltage, a heating current flows over a heating field formedby the heating layer. The connection electrodes can be implemented, forexample, in the form of strip or band electrodes, to introduce theheating current, as bus bars, widely distributed into the heating layer.Compared to the high-impedance heating layer, the connection electrodeshave a relatively low or low-impedance electrical resistance.

The arrangement also includes at least one temperature sensor, which isdisposed and implemented such that it can measure the temperature of thetransparent window, as well as an electronic control device coupled tothe temperature sensor and the voltage supply device, which is suitablyconfigured to carry out the method according to the invention(programmably). A control or regulating loop for the heating of thewindow is formed by the control device, the voltage supply device, andthe temperature sensor. Advantageously, a plurality of temperaturesensors are distributedly disposed on the window to be able to detectlocal temperature inhomogeneities of the window.

The temperature sensors are advantageously disposed in the edge regionof the window, in particular distributed over the edge region of thewindow, since, usually, greater temperature-induced stresses occurthere, such that the window breakage risk is increased. Advantageously,the temperature sensors are implemented in the form of printed conductoror measuring loops, which are produced, in particular, using a printingtechnique, for example, from the same material as the bus bars.

The method according to the invention is carried out on the basis of amanually or automatically activated de-icing process, with the de-icingprocess activated, for example, by a start signal. The start signal canbe generated manually by an operator, for example, by pressing on aswitch element, or automatically, for example, after starting the motorvehicle when certain conditions are present, such as low externaltemperatures below 0° C. It is understood that the method according tothe invention can include a step for starting the de-icing process, inparticular by generating a start signal. In the following, there is adescription of the process steps carried out for de-icing the windowwith an already started de-icing process.

The method according to the invention includes a process step (Step A),in which the window temperature is measured before the initialapplication of a heating voltage to the heating device. Here, thede-icing process is terminated before application of a heating voltageif the window temperature measured in Step A) is above a selectablelower temperature threshold value. The arrangement then automaticallytransitions into a standby or OFF state. Alternatively, for the casethat the window temperature measured in Step A) is equal to or less thanthe lower temperature threshold value, a heating voltage of a selectablesize is applied to the heating device for heating or de-icing the windowfor a heating period of a selectable duration. In the latter case, theStep B) described in the following is also executed.

The method according to the invention includes a further process step(Step B), in which the window temperature is measured after thebeginning of the heating period. In particular, the window temperatureis measured at the beginning of the heating period, for example, indefinable time intervals, advantageously continuously during the heatingperiod. Alternatively, the window temperature is measured afterexpiration of a waiting period of selectable duration after thebeginning of the heating period, i.e., after application of the heatingvoltage. The waiting period can even terminate during the heatingperiod. Alternatively, the waiting period can terminate with the heatingperiod or after expiration of the heating period. In Step B), thede-icing process is terminated if the window temperature reaches aselectable upper temperature threshold value. The arrangement thentransitions automatically into the standby or OFF state. If a waitingperiod for measuring the window temperature is provided and the waitingperiod terminates during the heating period, the heating voltage isturned off or the heating voltage is separated from the heating devicefor this purpose. If the waiting period terminates with or afterexpiration of the heating period, no further heating voltage is appliedto the heating device. Alternatively, for the case that the windowtemperature is lower than the upper temperature threshold value, thede-icing process is continued, with the Step C) described in thefollowing executed.

The method according to the invention includes a further process step(Step C), in which a heating voltage of selectable size is applied tothe heating device during a heating period of selectable duration. Inaddition, Step B) is repeated.

In the method according to the invention, the heating voltage in Step A)and in Step C) is more than 100 volts and the heating period is amaximum of 2 minutes, in particular a maximum of 90 seconds, and is, forexample, in the range from 30 to 90 seconds. As experiments of theapplicant have demonstrated, with this, for example, in motor vehiclewindshields, de-icing can be achieved reliably and safely withparticularly low electric power loss. The reason for this is reduceddissipation of energy due to a rapid heating of the window which—assurprisingly occurred—is not compensated by the higher electric power.With a view to a particularly low electric power loss, the heatingvoltage and heating period are selected such that a heating power of atleast 2 kilowatts (kW) per square meter (m²) of window area, preferablyat least 3 kW per m² of window area, is generated. In connection withthe fact that window heating is disabled when the window temperatureexceeds a lower temperature threshold value such that unnecessary windowheating is prevented, the draining of an energy storage device forsupplying the heating device can advantageously be further reduced.

By means of the method according to the invention, efficient de-icing ofa transparent window can be obtained, while simultaneously reliably andsafely avoiding heating of the window above the selectable uppertemperature threshold value. Depending on the selection of the uppertemperature threshold value, this advantageously enables preventingbreaking of the window or of connection elements, such as solder andadhesive connections due to large temperature changes. Thermally induceddamage of the window through the de-icing process can thus be prevented.On the other hand, with a correspondingly low upper temperaturethreshold value, it is possible for a person to avoid being burned ifthe heated window is deliberately or inadvertently touched. This isparticularly true for the method according to the invention, in which arelatively high heating voltage up more than 100 volts is applied for arelatively short time period of 1 to 120 seconds, in particular 30 to 60seconds, by means of which rapid de-icing of the window can be obtainedwith particularly low power loss, however, the risk of burns as well asthermal damage of the window exists if the window temperature is notsuitably limited.

In the method according to the invention, a plurality of (at least two)heating periods are advantageously carried out, i.e., one or a pluralityof Steps C) are provided such that a “pulsed” heating of the windowoccurs. By means of this measure, the window can be advantageouslyheated with a particularly low electric power loss.

In the method according to the invention, the heating periods in Step A)and Step C) can be the same length or have a duration different from oneanother. Likewise, the heating voltages applied during the heatingperiods in Step A) and Step C) can be the same size or have voltagevalues different from one another. With a particularly simple embodimentof the method according to the invention from a control and regulatingtechnology standpoint, the heating periods in Step A) and Step C) arethe same length and the heating voltages applied to the heating deviceare the same size.

In another advantageous embodiment of the method according to theinvention, in Step A) the duration of the heating period is selected asa function of the window temperature measured in Step A), with a shorterheating period selected in the case of a higher window temperature and alonger heating period selected in the case of a lower windowtemperature. This measure advantageously enables adaptation of theduration of the heating period in Step A) to the external ambienttemperature, which usually corresponds at least approximately to thewindow temperature before the initial application of a heating voltageand thus typically also represents a measure for the degree of icing ofthe transparent window such that a complete de-icing of the window canbe reliably and safely obtained even with severe icing.

In another advantageous embodiment of the method according to theinvention, in Step C) the duration of the heating period is selected asa function of the window temperature measured in Step B), with a shorterheating period selected in the case of a higher window temperature and alonger heating period selected in the case of a lower windowtemperature. This measure advantageously enables adaptation of theduration of the heating period in Step C) to the heating of the windowalready achieved such that due to a reduced or increased heat supply,the operational safety of the window can be even further improved. Inaddition, the heating power used for de-icing can be better dosed, withthe result that electrical energy can be conserved.

In the two embodiments of the method mentioned immediately above, afurther reduction in the draining of the energy storage device forsupplying the heating device can be particularly advantageously obtainedin connection with a relatively high feed voltage of more than 100 voltsand a relatively short heating period of a maximum of 2 minutes, inparticular of a maximum of 90 seconds, by means of which a low electricpower loss is obtained.

In another advantageous embodiment of the method according to theinvention, in Step A) the size of the heating voltage is selected as afunction of the window temperature measured in Step A), with a lowerheating voltage selected in the case of a higher window temperature anda higher heating voltage selected in the case of a lower windowtemperature. This measure advantageously enables adaptation of theheating voltage in Step A) to the external ambient temperature such thatthe heating power can be selectively adjusted and the electrical energyconsumed for de-icing can be reduced.

In another advantageous embodiment of the method according to theinvention, in Step C) the size of the heating voltage is selected as afunction of the window temperature measured in Step B), with a lowerheating voltage selected in the case of a higher window temperature anda higher heating voltage selected with a lower window temperature. Thismeasure advantageously enables adaptation of the heating voltage to theheating of the window already achieved such that the operational safetyof the window can be even further improved. In addition, the heatingpower used for de-icing can be better dosed, with the result thatelectrical energy can be conserved.

In the two embodiments of the method mentioned immediately above, afurther reduction in the draining of the energy storage device forsupplying the heating device can be particularly advantageously obtainedin connection with a relatively high feed voltage of more than 100 voltsand a relatively short heating period of a maximum of 2 minutes, inparticular a maximum of 90 seconds, by means of which a low electricpower loss is obtained. In connection with the embodiments, according towhich, in Step A) and/or in Step C), the duration of the heating periodis selected as a function of the window temperature, an even furtherreduction of the draining of the energy storage device for supplying theheating device can be obtained.

As already stated above, in Step B) the window temperature is measured,for example, after expiration of a waiting period after the beginning ofthe heating period. Advantageously, the window temperature is measuredimmediately after expiration of the heating period such that if thewindow is further heated, the de-icing of the window can occur withparticularly high efficiency.

In the method according to the invention, it is advantageous inpractical applications for 0° C. to be selected as the lower temperaturethreshold value such that a de-icing process is carried out only whenthe external ambient temperature is below the dewpoint. In addition, itis advantageous if the upper temperature threshold value is in the rangefrom 30° C. to 80° C., preferably in the range from 50° C. to 70° C.,and is, for example, 70° C. As a result of this, on the one hand, rapidde-icing can be obtained with low electric power loss. On the other,breaking of the window during de-icing as well as burning of a body partupon touching the window is reliably and safely avoided.

The invention further extends to a window arrangement with a transparentwindow, in particular a motor vehicle windshield, with an electricheating device, in particular a heating layer, which is connected to atleast two electrodes for connection to a voltage supply device such thatby applying a heating voltage, a heating current flows through theheating device. It further includes at least one temperature sensor formeasuring the window temperature, as well as a control device coupledwith the temperature sensor and the voltage supply device, which issuitably configured to carry out a method as described above.

In an advantageous embodiment of the window arrangement, the electrodesand the at least one temperature sensor, which can, in particular, bemade from the same material as the electrodes, are printed onto theheating device implemented in the form of a heating layer using aprinting technique. By means of this measure, the at least onetemperature sensor can be produced in series production, in aparticularly simple and economical manner. The at least one temperaturesensor is, for example, implemented in the form of a conductor loop ormeasuring loop.

In another advantageous embodiment of the window arrangement, aplurality of temperature sensors are provided, which are distributedlydisposed over the circumferential window edge or edge region of thewindow, preferably uniformly distributed, such that temperature changesin the particularly break-sensitive edge region of the window can bedetected.

In another advantageous embodiment of the window arrangement, atemperature sensor is, in each case, disposed in window regions in whichlocal overheating can occur, for example, end sections of separatinglines or heating-layer-free zones, such that temperature changes inthese particularly break-sensitive regions of the window can bedetected.

The invention further extends to the use of a window of the arrangementaccording to the invention as described above as a functional individualpiece and as a built-in part in furniture, devices, and buildings, aswell as in means of transportation for travel on land, in the air, or onwater, in particular in motor vehicles, preferably in electric vehicles,in particular as a windshield, rear window, side window, and/or glassroof.

It is understood that the different embodiments can be realizedindividually or in any combinations. In particular, the aforementionedcharacteristics and those to be explained in the following can be usednot only in the combinations indicated, but also in other combinationsor alone, without departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now explained in detail using exemplary embodimentswith reference to the accompanying figures. They depict, in simplified,not-to-scale representation:

FIG. 1 a schematic view of an exemplary embodiment of the arrangementaccording to the invention with a motor vehicle windshield;

FIG. 2 a schematic cross-sectional view of the motor vehicle windshieldof FIG. 1;

FIG. 3 a flowchart of an exemplary embodiment of the method according tothe invention for de-icing the motor vehicle windshield of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is first made to FIGS. 1 and 2, in which a window arrangementaccording to the invention, referred to as a whole by the referencecharacter 1, is illustrated. The window arrangement 1 includes atransparent windshield 2 of a motor vehicle, preferably of an electricmotor vehicle, which is implemented here, for example, as a compositewindow.

As can be discerned from the cross-sectional depiction of FIG. 2, thewindshield 2 has a rigid outer pane 3 and a rigid inner pane 4, whichare both implemented as individual panes and are fixedly bonded to eachother via a thermoplastic adhesive layer 5. The two individual panes 3,4 are approximately the same size, have a roughly trapezoidal curvedcontour, with the understanding that the invention is not restricted tothis, but rather that the windshield 2 can have any other shape suitedfor the practical application. The two individual panes 3, 4 are made ofa glass material, such as float glass, cast glass, or ceramic glass or anon-glass material, for example, plastic, in particular polystyrene(PS), polyamide (PA), polyester (PE), polyvinyl chloride (PVC),polycarbonate (PC), polymethyl methacrylate (PMA), or polyethyleneterephthalate (PET). In general, any material with sufficient chemicalresistance, suitable shape and size stability, as well as adequateoptical transparency can be used. Plastic, in particular based onpolyvinyl butyral (PVB), ethylene vinyl acetate (EVA), and polyurethane(PU), can, for example, be used as an adhesive layer 5 for bonding thetwo individual panes 3, 4. For an application other than as awindshield, it would also be possible to produce the two individualpanes 3, 4 from a flexible material.

The contour of the windshield 2 is defined by a circumferential windowedge 6, which is composed corresponding to the trapezoidal shape of twolong window edges 6 a, 6 a′ (top and bottom in the installationposition) and two short window edges 6 b, 6 b′ (left and right in theinstallation position).

A transparent heating layer 7 serving for electric heating of thewindshield 2 is deposited on the side of the inner pane 4 bonded to theadhesive layer 5 (“side 3”). The heating layer 7 is appliedsubstantially on the entire surface of the inner pane 4, with an edgestrip 8 of the inner pane 4 circumferential on all sides not coated suchthat a heating layer edge 9 is set back inward relative to the windowedge 6. This measure serves for electrical isolation of the heatinglayer 7 toward the outside. In addition, the heating layer 7 isprotected against corrosion penetrating from the window edge 6. It wouldalso be possible not to apply the heating layer 7 on the inner pane 4,but instead to apply it on a large-area carrier, which is subsequentlyadhered to the individual panes 3, 4. Such a carrier can, in particular,be a plastic film, made for example of polyamide (PA), polyurethane(PU), polyvinyl chloride (PVC), polycarbonate (PC), polyester (PE), orpolyvinyl butyral (PVB).

The heating layer 7 includes an electrically conductive material.Examples of this are metals with high electrical conductivity such assilver, copper, gold, aluminum, or molybdenum, metal alloys such assilver alloyed with palladium, as well as transparent, conductive oxides(TCOs). TCOs are preferably indium tin oxide, fluoride-doped tindioxide, aluminum-doped tin dioxide, gallium-doped tin dioxide,boron-doped tin dioxide, tin zinc oxide, or antimony-doped tin oxide.The heating layer 7 can consist of one conductive individual layer or alayer structure that includes at least one conductive sublayer. Forexample, such a layer structure includes at least one conductivesublayer, preferably silver (Ag), and other sublayers, such asanti-reflection and blocker layers.

The thickness of the heating layer 7 can vary widely, with the thicknessat every point being, for example, in the range from 30 nm to 100 μm. Inthe case of TCOs, the thickness is, for example, in the range from 100nm to 1.5 μm, preferably in the range from 150 nm to 1 μm, and even morepreferably in the range from 200 nm to 500 nm. Advantageously, theheating layer 7 has high thermal stability such that it withstands thetemperatures of typically more than 600° C. necessary for the bending ofglass without functional degradation. However, even a heating layer 7with low thermal stability, which is applied after the bending of theglass pane, can be provided. The sheet resistance of the heating layer 7is preferably less than 20 ohm and is, for example, in the range from0.1 to 20 ohm. In the exemplary embodiment depicted, the sheetresistance of the heating layer 7 is, for example, in the range from 1to 5 ohm.

The heating layer 7 is, for example, deposited from the gas phase, forwhich purpose methods known per se, such as chemical vapor deposition(CVD) or physical vapor deposition (PVD), can be used. Preferably, theheating layer 7 is deposited by sputtering (magnetron cathodesputtering).

The windshield 2 must be adequately transparent to visible light in thewavelength range from 350 nm to 800 nm, with the term “transparency”understood to mean light transmittance of more than 80%. This can beobtained, in particular, by means of individual panes 3, 4 made of glassand a transparent heating layer 7 made of silver (Ag).

The surface of the outer pane 3 facing the inner pane 4 is provided withan opaque color layer that forms a frame-shaped circumferential maskingstrip 10 on the window edge 6. The masking strip 10 is made, forexample, of an electrically insulating, black-colored material that isbaked into the outer pane 3. On the one hand, the masking strip 10prevents seeing an adhesive strand (not shown), with which thewindshield 2 is glued into the motor vehicle body; on the other, itserves as UV protection for the adhesive material used. Moreover, themasking strip 10 defines the visual field of the windshield 2. A furtherfunction of the masking strip 10 is to conceal the two bus bars 11, 12such that they are not discernible from the outside.

The heating layer 7 is electrically connected to a first bus bar 11 anda second bus bar 12. The two bus bars 11, 12 are, in each case,implemented band-shaped or strip-shaped and serve as connectionelectrodes with a broad introduction of a feed current into the heatinglayer 7. For this, the bus bars 11, 12 are disposed on the heating layer7, with the first bus bar 11 extending along the upper long window edge6 a and the second bus bar 12 extending along the lower long window edge6 a′. The two bus bars 11, 12 are made from the same material and can beproduced, for example, by printing a silver printing paste onto theheating layer 7, for example, using a screen printing method.Alternatively, it would also be possible to produce the bus bars 11, 12from narrow metal foil strips made, for example, of copper or aluminum.These can, for example, be fixed on the adhesive layer 5 and disposed onthe heating layer 7 at the time of the bonding of the outer and innerpane 3, 4. In this process, an electrical contact can be ensured throughthe action of heat and pressure at the time of the bonding of theindividual panes 3, 4.

The first bus bar 11 is connected via a connection line (not shown indetail), which is, for example, implemented as a flat-band conductor(e.g., narrow metal foil), and a power line 19 to one terminal (forexample, negative terminal) of a voltage source 14 to supply a feedvoltage. Analogously, the second bus bar 12 is connected via aconnection line (likewise not shown in detail) and a power line 19 tothe other terminal (for example, positive terminal) of the voltagesource 14. By means of the two bus bars 11, 12, a heating field 13 isenclosed, in which upon application of a feed voltage, a heating currentflows. The voltage source 14 can be, for example, a battery oraccumulator, in particular a motor vehicle battery, or a transformercoupled to a battery. Preferably, the voltage source 14 is implementedsuch that a feed voltage of more than 100 volts, is made available,which can be the case, in particular with batteries of electricvehicles.

The arrangement 1 also has a plurality of distributedly disposedtemperature sensoren 15, with only one temperature sensor 15 depicted inFIG. 1. The temperature sensors 15 are, for example, disposed on theoutward side of the outer pane 3 or on the inward side of the inner pane4, with it being, however, also conceivable for the temperature sensors15 to be disposed between the two individual panes 3, 4. By means of theplurality of temperature sensors 15, the temperature of the windshield 2can be detected. The temperature sensors 15 are widely distributed onthe windshield 2 such that, in particular, even locally different windowtemperatures can be detected well. Typically, windshields haverelatively low heat conductivity. Local temperature differences candevelop, for example, through sun shining on a subregion of thewindshield 2.

Advantageously, a plurality of temperature sensors 15 is distributedlydisposed on the heating layer edge 9 or window edge 6, preferablyuniformly distributed, since temperature differences on the window edge6 due to high local voltages are associated with a relatively high riskof breakage during de-icing. For example, a temperature sensor 15 isdisposed, in each case, at the four corners of the windshield 2, as wellas on the window edge 6 in the center between two corner temperaturesensors 15. Moreover, it is advantageous for temperature sensors to bedisposed, in each case, in the window regions in which local overheating(“hot spots”) can occur. These are, in particular, heating-layer-freezones, for example, communication windows or end sections of separatinglines for the structuring of the heating layer 7.

The temperature sensors 15 can be implemented in many ways, for example,as thermocouples. From a process technology standpoint, it isparticularly advantageous for the temperature sensors 15 to beimplemented as measuring loops that are printed on the window, inparticular on the heating layer 7, which can then be contacted from theoutside. This enables making the temperature sensors 15 from one and thesame material (for example, silver printing paste) as the two bus bars11, 12. It is merely necessary to ensure that the material of themeasuring loops has a temperature sensitive electrical resistance.

The temperature sensors 15 are, in each case, connected for datatransfer via a data line 17 to a microprocessor-based control device 16.The control device 16 is further connected via a data line 17 to aswitching device/converter 18 associated with the voltage source 14,which switching device/converter 18 is connected to the two power lines20 and serves to electrically connect the voltage source 14 to theheating layer 7 or to separate it therefrom. In the present exemplaryembodiment, the switching device/converter 18 serves not only for theconnection of the feed voltage but also for conversion of the feedvoltage. For this, the switching device/converter 18 is implemented as avoltage converter to increase or reduce the feed voltage supplied by thevoltage source 14. The switching device/converter 18 and the voltagesource 14 form together a voltage supply device for the heating layer 7of the windshield 2. It is understood that the switchingdevice/converter 18 can also be implemented as a switching devicewithout a voltage conversion function. It is likewise possible for theswitching device/converter 18 to be integrated into the voltage source14.

The data lines 17 can be implemented with a wired or wirelessconnection. By means of the control device 16 and the devices coupled bythe data lines 17, a control or regulating loop for de-icing thewindshield 2 is formed, by means of which the feed or heating voltageprovided by the voltage source 14 can be applied to the heating layer 7optionally based on sensor signals of the temperature sensors 15 and canbe converted if need be. The control device 16 is configured from aprogramming standpoint such that the method for de-icing the windshield2 described in the following can be executed.

FIG. 3 presents a flow chart or process diagram to illustrate anexemplary method. A concrete de-icing process for de-icing the window 2is, in this case, activated or started manually by operating a switchingelement (not shown) in a control console of the motor vehicle. It wouldalso be conceivable to start the de-icing process automatically, forexample, upon starting the engine and detection of a low outsidetemperature below a specified threshold value, for example, 0° C., bymeans of an outside temperature sensor. A start signal can, for example,be generated manually or automatically to activate the de-icing process.

If a de-icing process has been activated, the temperature T of thewindshield 2 is still measured before the initial application of aheating voltage to the heating layer 7 (I). If the temperature T of thewindshield 2 on only one temperature sensor 15 exceeds a selectablelower temperature threshold value, here, for example, 0° C., (II), noheating voltage is applied to the heating layer 9 and the method orde-icing process is terminated (III). For this purpose, a stop signalcan, for example, be generated. The window arrangement then transitionsinto a standby or OFF state. If, alternatively, the temperature T of thewindshield 2 equals or is less than the lower temperature thresholdvalue, here, for example, 0° C. (IV), the feed voltage of more than 100volts, for example, 118 volts, supplied by the voltage source 14 isapplied to the heating layer 7 for a period of, for example, 1 to 120seconds, in particular 30 to 90 seconds (V).

Then, the temperature of the windshield 2 is measured after thebeginning of the heating period, i.e., after application of the feedvoltage. This occurs, for example, in definable time intervals beginningwith the application of the feed voltage, advantageously continuously.Alternatively, the temperature of the windshield 2 is measured by thetemperature sensors 15 immediately after expiration of the time periodof the application of the feed voltage, i.e., after a waiting period of,for example, 1 to 120 seconds, in particular 30 to 90 seconds (VI).

If the temperature T of the windshield 2 on only one temperature sensor15 corresponds to a selectable upper temperature threshold value, here,for example, 70° C. (VII), the de-icing process is terminated (VIII).For this purpose, a stop signal can, for example, be generated. Thewindow arrangement then transitions into a standby or OFF state. For thecase in which the temperature of the windshield 2 is still measuredduring the time period of the application of the feed voltage, the feedvoltage is, for this purpose, separated from the heating layer 7 by theswitching device/converter 18. If the temperature T of the windshield 2is less than the upper temperature threshold value (IX), here, forexample, 70° C., the same heating voltage as previously is applied tothe heating layer 7 in the form of a regulating loop (V). Again, thetemperature of the windshield 2 is measured after the beginning of theheating period, i.e., after application of the feed voltage. This canoccur, as previously, for example, in definable time intervals beginningwith the application of the feed voltage, advantageously continuously.Alternatively, the temperature of the windshield 2 is measuredimmediately after expiration of the time period of the application ofthe feed voltage (VI), with, on the basis of the measured temperature,the de-icing process terminated or the heating voltage is again applied,according to the criteria immediately above. The application of theheating voltage (V) and the measurement of the window temperature (VI)are, if need be, repeated until the temperature of the windshield 2 onat least one temperature sensor 15 corresponds to the upper thresholdvalue. Alternatively, it would also be conceivable to limit the de-icingprocess to a maximum number of heating periods. Finally, the arrangement1 transitions into a standby or OFF state until the start of the nextde-icing process, for example, by means of the generation of the stopsignal.

In the exemplary embodiment, the duration of the first heating periodand the heating voltage during the first heating period can be adjustedas a function of the window temperature measured at the beginning of thede-icing process. Likewise, the duration of each subsequent (second,third, . . . ) heating period and the heating voltage during thesubsequent heating periods can be adjusted as a function of the windowtemperature measured immediately before the beginning of the respectiveheating period. Advantageously, to conserve electrical heating power inthe case of a higher window temperature, a shorter heating period is setand with a lower window temperature, a longer heating period is set.Advantageously, to conserve electrical heating power in the case of ahigher window temperature, a lower feed voltage, corresponding to lowerelectrical power is set, and with a lower window temperature, a higherfeed voltage, corresponding to higher electrical power is set.

In the exemplary embodiment, the heating voltages and the heating arethe same. However, in accordance with the above statements, it wouldalso be conceivable for the feed voltage applied to the heating layer 7in the second and subsequent heating periods to be adjusted as afunction of the measured window temperature used in the previous query.Advantageously, to conserve electrical heating power in the case of ahigher window temperature, a lower heating voltage is set, and with alower window temperature, a higher heating voltage is set by means ofthe switching device/converter 18. It would also be conceivable for theduration of the second and subsequent heating periods to be adjusted asa function of the measured temperature of the windshield 2 used in theprevious query. Advantageously, to conserve electrical heating power inthe case of a higher window temperature, a shorter heating period isset, and with a lower window temperature, a longer heating period isset.

As already stated, preferably, a heating voltage of more than 100 volts,here, for example, 118 volts, is applied to the heating layer 7 for arelatively short period of time of 1 to 120 seconds, for example, 30 to90 seconds, as a result of which de-icing of the windshield 2 can beobtained with a low electric power loss. Preferably, the heating voltageand the heating period are selected such that a heating power of atleast 2 kW per m² of window area, in particular at least 3 kW per m² ofwindow area, is generated.

The following table presents measurement data obtained in practicalexperiments with the de-icing of a conventional motor vehicle windshield2 in a climate chamber at an ambient temperature of −10° C. For this, anidentical film of ice was applied to the windshield with an air knife ineach case under identical conditions. Then, the window was de-iced usingthe method described above.

TABLE Experiment P[W] U[V] t[s] E[Wh] No. 1 600 40 630 105 No. 2 4720118 60 79

Accordingly, in a first experiment (No. 1), a feed voltage U of 40 volts(V) was applied for a period of 630 seconds(s) to the heating layer 7 ofthe windshield 2, by means of which complete de-icing of the window waseffected. In this case, electrical energy of 105 watt hours (Wh) wasconsumed, corresponding to an electrical output of 600 watts (W).

Then, in a second experiment (No. 2), a feed voltage U of 118 volts (V)was applied for a period of 60 seconds (s) to the heating layer 7 of thewindshield 2, by means of which complete de-icing of the window waslikewise effected. In this case, electrical energy of only 75 watt hours(Wh) was consumed, corresponding to an electrical output of 4720 watts(W).

These experiments surprisingly demonstrated that with a higher feedvoltage and a shorter heating period, significantly less electricalenergy is consumed (in the two experiments approx. 25% less) and theelectrical output is many times higher. In particular, with equalelectrical work, by generating a higher electrical output for a shorterperiod of time, de-icing of the windshield can be obtained with a lowerelectric power loss.

LIST OF REFERENCE CHARACTERS

-   1 window arrangement-   2 windshield-   3 outer pane-   4 inner pane-   5 adhesive layer-   6 window edge-   6 a, 6 a′ long window edge-   6 b, 6 b′ short window edge-   7 heating layer-   8 edge strip-   9 heating layer edge-   10 masking strip-   11 first bus bar-   12 second bus bar-   13 heating field-   14 voltage source-   15 temperature sensor-   16 control device-   17 data line-   18 switching device/converter-   19 power line

1. A window arrangement, comprising: a transparent window having anelectric heating device, wherein the electric heating device isconnected to at least two electrodes provided for connection to avoltage supply device such that, by applying a heating voltage, aheating current flows through the electric heating device, at least onetemperature sensor for measuring a window temperature, and a controldevice coupled with the at least one temperature sensor and the voltagesupply device, wherein the control device is suitably configured tocarry out a method for de-icing the transparent window with the electricheating device on a basis of a manual or automatically initiatedde-icing process.
 2. The window arrangement according to claim 1,wherein the at least two electrodes and the at least one temperaturesensor are printed onto the heating device implemented in the form of aheating layer using a printing technique.
 3. The window arrangementaccording to claim 1, wherein a plurality of temperature sensors aredistributedly disposed over a window edge.
 4. The window arrangementaccording to claim 1, wherein the at least one temperature sensor is, ineach case, disposed in a window region wherein local overheating canoccur.
 5. The window arrangement according to claim 4, wherein thewindow region wherein local overheating can occur is a end section ofseparating lines or a heating-layer-free zone.
 6. The window arrangementaccording to claim 1, wherein the transparent window comprises a vehiclewindshield.
 7. The window arrangement according to claim 1, wherein theelectric heating device comprises a heating layer.
 8. The windowarrangement according to claim 7 wherein the heating layer comprises a aheating field formed between the electrodes.
 9. The window arrangementaccording to claim 1, wherein the method comprises the following steps:Step A): measuring a window temperature before an initial application ofa first heating voltage of more than 100 volts, wherein i) the method isterminated when the window temperature exceeds a lower temperaturethreshold value, ii) or the first heating voltage of more than 100 voltsis applied to the heating device over a first heating period of amaximum of 2 minutes, when the window temperature is equal to or lessthan the lower temperature threshold value, and wherein the firstheating voltage and the first heating period are selected such that afirst heating power of at least 2 kilowatts (kW) per square meter (m²)of window area is generated, and step B) is executed; Step B): measuringthe window temperature after a beginning of the first heating period,wherein a de-icing process iii) is terminated when the windowtemperature reaches an upper temperature threshold value, iv) or step C)is carried out when the window temperature is lower than the uppertemperature threshold value; and Step C): applying a second heatingvoltage of more than 100 volts to the heating device over a secondheating period of a maximum of 2 minutes with the second heating voltageand the second heating period selected such that a second heating powerof at least 2 kilowatts (kW) per square meter (m²) of window area isgenerated, and repeating step B); wherein in step A), duration of thefirst heating period is selected as a function of the window temperaturemeasured in step A), with a shorter first heating period selected incase of a higher window temperature and a longer first heating periodselected in case of a lower window temperature; and wherein in step C)duration of the second heating period is selected as a function of thewindow temperature measured in step B), with a shorter second heatingperiod selected in case of a higher window temperature and a longersecond heating period selected in case of a lower window temperature.